LASER CVD VS HOT-WALL CVD - COATING OF FIBERS FOR CERAMIC COMPOSITES

Based on a technological 5 kW cw-CO2 laser, an atmospheric pressure la ser assisted CVD process has been established which performs a continu ous high rate coating of carbon fibre rovings. Layers of pyrolytic car bon have been deposited from CH4 with a rate of 0.6 mu m/s which enhan ces the tensile strength and Weibull modulus of fibres. In another var iant, pyro-C layers have been deposited in a technological thermal hot -wall CVD reactor on fabrics and on preforms. The layer thickness is u niform over the cross section of the fibre bundles, but variations in flow direction have been detected. Composite materials with SiC matrix have been processed by both liquid precursor infiltration using Si-po lymers and by converting a carboneous matrix being infiltrated with li quid silicon. Preforms with uncoated and coated fibres have been infil trated. The resulting composites are characterized by high tensile str ength and crack resistance due to the favourable pull-out behaviour of coated fibres.